The present invention relates to a method for measuring the volume of solid and liquid in a suspension, such as counting the total volume of blood cells in a patient's blood or the total volume of particulate contaminants in a sample of drinking water. More specifically, the present invention relates to a method of measurement of the actual volume of liquid and/or the actual volume of solids in a liquid suspension.
In my earlier patents (U.S. Pat. Nos. 4,614,722; 4,788,155 and 5,147,785 the disclosures of which are hereby incorporated by reference), I disclosed methods for testing a subject's blood for various maladies, including allergies. The described testing of the blood permits the diagnosis of the maladies by preparing two samples of the subject's blood.
The first sample is a control sample, and the second is a test sample. A test substance having a predetermined relationship with the malady under consideration is placed into the test sample, and the blood and the substance are given the opportunity to react. The blood cells in the two samples are counted and compared, both as to number and size-distribution. If a significant difference is observed between the blood cells present in the two samples, then it may be concluded that the subject has the malady for which he was tested.
In the performance of my patented tests, I have needed to use various apparatus for counting and sizing particles, and been disappointed in inaccuracies that I have found. I have attributed the inaccuracies, in part, to the fact that my prior testing would not recognize small, subtle, changes in the size of a patient's blood cells. I therefore saw the need to develop a more accurate and reliable method of performing three-dimensional volumetric measurement of blood cells in a patient's blood. After working on such an apparatus, I also saw that it would have general applicability in other fields for measuring particles in a suspension, such as in water plants where the measurement of particulate contaminants is of serious importance, or in paint manufacturing where consistency of product is important. In short, the inventive method could have a widespread utility in the field of volumetric measurement of particles in suspensions.
Previously, attempts to count and size particles in a fluid involved methods which included individual counts of the solid particles which were triggered by deviations from a constant baseline voltage. Once the voltage deviated from the baseline, a second measurement would be taken at a predetermined interval which was intended to represent the maximum voltage, indicative of the size of the particle.
This method is faulty for a few reasons.
First, even though the rate of travel of the fluid through the aperture is known, there is no guarantee that the predetermined interval is correct. If the particle enters at an angle, for example, the measurement may be off.
Second, measurement of the initial peak of the deviation as the correct volume of the particle may not be accurate, since some particles (depending upon their angle of entry into the aperture) might have an initial deviation which is far greater than the deviation which indicates their actual volume.
Third, where the actual baseline potential differs from the presumed static baseline potential, inaccuracies develop in measuring the particle's volume, since the measurement of the volume of the particle is derived from the comparison of the deviation of the potential from an incorrect baseline starting point.
Fourth, by limiting counting to only those particles which cause a potential deviation greater than a predetermined threshold, you lose the count of actual particles which are too small to cause deviations greater than the threshold.
It was my desire, therefore, to develop a new procedure for performing the volumetric measurement of solids in a suspension, of any kind, in many different types of fluids, more accurately than heretofore known.